Scandium, although quite abundant, is a relatively unutilized element partly because there are no convenient (high grade) sources of the metal. Therefore, fulfillment of scandium's technological promise in such fields as alloys, ceramics, phosphors, etc. awaits a readily available economical source of the material.
Important low level sources of scandium include uranium tailings and the waste sludges of tungsten recovery plants which process ores such as scheelite and wolframite. The sludge from such plants consists largely of mixed manganese, iron and other hydrous oxides with varying levels of scandium, typically in the range of 100-1000 ppm.
Processes which attempt to recover scandium from such a material face the problem that the waste is extremely complex and heterogeneous chemically. About two dozen other elements are present in greater or lesser amounts. Furthermore, the low level of scandium present mandates processing large quantities of the sludge. Patented procedures for the separation of scandium from trivalent iron and other metals have disadvantages which make them ill-suited to the large scale production of scandium. For instance, an extraction-based procedure (U.S. Pat. No. 3,013,859) requires that 2.5 lbs/gal of magnesium nitrate be added to the aqueous phase before equilibration with the alkyl phosphate extractant. On the large scale such a procedure would be both expensive, requiring large quantities of magnesium nitrate, and would introduce the problem of disposing or recovering the magnesium nitrate.
Another patented procedure (U.S. Pat. No. 2,874,039) involves the separation of scandium from iron and other metals by volatilization of the chlorides in a furnace at about 1000.degree. C. Such a procedure would be high in energy consumption and low in throughput.
The procedure of the instant invention on the other hand eliminates these objections.